The term “noncoordinating anion” (NCA) is now accepted terminology in the field of olefin and vinyl molecule, coordination, insertion, and carbocationic polymerization. See, for example, EP 0 277 003, EP 0 277 004, U.S. Pat. Nos. 5,198,401, 5,278,119, and Baird, Michael C., et al, J. Am. Chem. Soc. 1994, 116, 6435-6436. The noncoordinating anions are described to function as electronic stabilizing cocatalysts, or counterions, for active, cationic metallocene polymerization catalysts. The term noncoordinating anion applies both to truly noncoordinating anions and to coordinating anions that are labile enough to undergo replacement by olefinically or acetylenically unsaturated molecules at the insertion site. These noncoordinating anions can be effectively introduced into a polymerization medium as Bronsted acid salts containing charge-balancing countercations, as ionic cocatalyst compounds, or mixed with an organometallic catalyst before adding it to the polymerization medium. See also, the review articles by S. H. Strauss, “The Search for Larger and More Weakly Coordinating Anions,” Chem. Rev., 93, 927-942 (1993).
U.S. Pat. No. 5,502,017, to Marks et al., addresses ionic metallocene catalysts for olefin polymerization containing a weakly coordinating anion comprising boron substituted with halogenated aryl substituents preferably containing silylalkyl substitution, such as a t-butyldimethyl-silyl substitution. Marks et al. disclose the weakly coordinating anion as the cocatalyst. The silylalkyl substitution is said to increase the solubility and thermal stability of the resulting metallocene salts. Examples 3-5 describe synthesis of and polymerization with the cocatalyst compound triphenylcarbenium tetrakis (4-dimethyl-t-butylsilyl-2,3,5,6-tetrafluorophenyl) borate.
In view of the above, there is a continuing need for olefin polymerization activators both to improve the industrial economics of solution polymerization and to provide alternative activating compounds for ionic, olefin polymerization catalyst systems.